The present invention relates to a laminated member comprising a polyethylene resin composition layer having a very high adhesive strength to a substrate, and a method for manufacturing the same. More particularly, the present invention can provide a laminated member having a high adhesive strength without using an anchor-coating agent by using a specific polyethylene resin composition having excellent physical properties such as adhesion properties, and process ability. The present invention also relates to a method for manufacturing the laminated member, which is capable of high-speed molding at low temperature because the polarity of the surface to be treated can be remarkably enhanced by using such a specific polyethylene in combination with an ozone treatment and/or a corona discharge treatment in a extrusion-lamination molding method.
This application is based on the patent application (Japanese Patent Application No. Hei 10-279200) filed in Japan, the disclosure of which is incorporated in part into the present application.
It has hitherto been performed that polyethylene polymers such as polyethylene and ethylene-vinyl acetate copolymer are extrusion-laminated on substrates such as various films made of plastics (e.g. polypropylene, polyamide, polyester, and saponified ethylene-vinyl acetate copolymer), aluminum foil, Cellophane, and paper, thereby to provide the resulting laminate products with heat-sealing properties and moisture resistance. A large amount of these laminate products are used generally as packaging materials.
In extrusion-lamination molding, polyethylene polymers must possess high adhesion properties to various substrates, as a routine requirement. However, an ethylene polymer is essentially inferior in adhesion properties to the polar substrates described above because it is a non-polar resin. Therefore, when a low-density polyethylene formed according to a high-pressure radical polymerization method (hereinafter abbreviated to xe2x80x9cLDPExe2x80x9d) is extrusion-laminated on the substrate, the adhesion properties to the substrate are improved by usually setting the resin temperature to a high temperature of 310xc2x0 C. or higher, thereby oxidizing the surface of a thin melt resin film extruded from an extruder. However, oxidative aging of LDPE is caused by raising the resin temperature to 310xc2x0 C. or higher, as described above. As a result, the influence of a high degree of fumes causes a deleterious change in the working and surrounding environments. Other problems also arise such as deterioration of the quality of laminate products due to oxidation at high temperature, odor, and high cost of producing heat-seal layer. In addition, when molding is performed at high speed to improve productivity, the adhesive strength is lowered.
In the case of an ethylene-vinyl acetate copolymer, when the extrusion resin temperature is raised to 280xc2x0 C. or higher, the ethylene-vinyl acetate copolymer decomposes in an extruder or a die causing a strong acetic acid odor and bubble formation. Therefore, it is necessary to extrude the resin at a temperature of 260xc2x0 C. or lower.
However, in the case of such a low temperature, the resulting adhesive strength to the substrate is not sufficient to make it suitable for practical use. To cope with such a problem, a method has been used, wherein LDPE is previously extrusion-laminated on a substrate at high temperature of 310xc2x0 C. or higher and an ethylene-vinyl acetate copolymer is extrusion-laminated on the surface of LDPE at the same temperature as described above. Therefore, there have been problems such as complicated processes and economical disadvantages.
Japanese Patent Application, First Publication No. Sho 57-157724 discloses a method for extruding an polyethylene resin at low temperature within a range from 150 to 290xc2x0 C. and subjecting it to ozone treatment, and pressure-laminating the polyethylene resin on a substrate, wherein the surface to be treated has been subjected to an anchor-coating treatment.
When the molding temperature is lowered like this method, fumes and odor are reduced, thereby solving these problems. However, large problems related to productivity and economical efficiency still remain, for example, the adhesive strength is lowered because the molding temperature is lowered, and it is difficult to increase molding speed and reduce the thickness.
When the resin temperature is raised to solve the problems described above, concomitant problems also arise such as exacerbating the influence of fumes on the working and surrounding environments, and deterioration in the odor of products due to oxidative aging at high temperature.
Since high-speed mold ability is now required, the resin temperature must be raised even further to increase the molding speed while still securing high adhesion properties, and, as a result, the problems described above become serious. In addition, even when using the ozone treatment to achieve high-speed molding, it has been difficult to obtain sufficient adhesion properties.
The present invention has been made to solve the problems described above and provides a method for manufacturing a laminated member, which can maintain adhesive strength to a different kind of a substrate within a range from low temperature to high temperature by using a specific polyethylene resin composition, which can reduce the resin temperature during the extrusion-lamination molding process and can inhibit noxious influences such as fumes and odor on the working and surrounding environments particularly by using said specific polyethylene resin composition in combination with an ozone treatment, and which also can improve the high-speed mold ability without raising the resin temperature, though it is capable of molding at a molding temperature within a range from 200 to 300xc2x0 C. (wide range from low temperature to high temperature), and the laminated member.
The present inventors have conducted intensive studies to solve the problems described above. As a result, they have found that the problems described above can be solved by incorporating a specific amount of a compound having a specific structure into a general polyethylene resin, thus completing the present invention.
That is, the laminated member of the present invention is a laminated member comprising a substrate and a layer formed on at least one surface of said substrate, said layer being made of a polyethylene resin composition containing a polyethylene resin (A) and a compound having intramolecular unsaturated bonds (B), the number of intramolecular unsaturated bonds in said polyethylene resin composition being not less than 0.5 per 103 carbon atoms.
The polyethylene resin composition preferably contains 99.9 to 50% by weight of the polyethylene resin (A) and 0.1 to 50% by weight of the compound having intramolecular unsaturated bonds (B). In the compound having intramolecular unsaturated bonds (B), the number of intramolecular unsaturated bonds is preferably within a range from 0.5 to 250 per 103 carbon atoms.
The compound having intramolecular unsaturated bonds (B) is preferably at least one selected from polybutadiene, ethylene-propylene-diene terpolymer (EPDM) and polyisoprene. Among these compounds, 1,2-polybutadiene is particularly preferred.
The method for manufacturing a laminated member of the present invention comprises the step of laminating and adhering these polyethylene resin compositions on at least one surface of a substrate by extrusion-lamination method.
In that case, the polyethylene resin composition film subjected to an ozone treatment and the substrate subjected to a corona discharge treatment are preferably laminated and adhered through the surface-treated surface.
Molding can be performed at a molding temperature within a wide range from low temperature to high temperature, e.g. 300xc2x0 C. or lower, and preferably from 200 to 300xc2x0 C. High-speed molding can be performed even within a low temperature range (from 230 to 270xc2x0 C.).